[Intel-gfx] [PATCH] drm/i915: enable trickle feed on Haswell

[Paulo Zanoni]

From: Paulo Zanoni <paulo.r.zanoni at intel.com>

We shouldn't disable the trickle feed bits on Haswell. Our
documentation explicitly says the trickle feed bits of PRI_CTL and
CUR_CTL should not be programmed to 1, and the hardware engineer also
asked us to not program the SPR_CTL field to 1. Leaving the bits as 1
could cause underflows.

Reported-by: Arthur Runyan <arthur.j.runyan at intel.com>
Signed-off-by: Paulo Zanoni <paulo.r.zanoni at intel.com>
---
 drivers/gpu/drm/i915/i915_reg.h      |  1 +
 drivers/gpu/drm/i915/intel_display.c | 10 +++++++---
 drivers/gpu/drm/i915/intel_pm.c      |  2 --
 drivers/gpu/drm/i915/intel_sprite.c  |  7 +++++--
 4 files changed, 13 insertions(+), 7 deletions(-)

Some side discussions:

 1 - It seems we always do read-modify-write with the PRI/SPR/CUR registers. I
 think this is dangerous since we may forget to disable something and keep our
 code in a bugged state forever. Shouldn't we try to completely set the full
 state of the bits from scratch every time we enable PRI/SPR/CUR?

 2 - We also have code to enable the trickle feed bits at init_clock_gating.
 Isn't this dangerous? Trickle fee changes the memory is read, my first guess
 would be that it's probably not safe to change this bit when things are
 enabled. Also, we lose the state of these bits when the power well is disabled,
 so the code in init_clock_gating really makes no sense on Haswell.

diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
index bbbc177..e92bb47 100644
--- a/drivers/gpu/drm/i915/i915_reg.h
+++ b/drivers/gpu/drm/i915/i915_reg.h
@@ -3312,6 +3312,7 @@
 #define   MCURSOR_PIPE_A	0x00
 #define   MCURSOR_PIPE_B	(1 << 28)
 #define   MCURSOR_GAMMA_ENABLE  (1 << 26)
+#define   CURSOR_TRICKLE_FEED_DISABLE	(1 << 14)
 #define _CURABASE		(dev_priv->info->display_mmio_offset + 0x70084)
 #define _CURAPOS		(dev_priv->info->display_mmio_offset + 0x70088)
 #define   CURSOR_POS_MASK       0x007FF
diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index c64631d..d5f038e 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -2077,8 +2077,10 @@ static int ironlake_update_plane(struct drm_crtc *crtc,
 	else
 		dspcntr &= ~DISPPLANE_TILED;
 
-	/* must disable */
-	dspcntr |= DISPPLANE_TRICKLE_FEED_DISABLE;
+	if (IS_HASWELL(dev))
+		dspcntr &= ~DISPPLANE_TRICKLE_FEED_DISABLE;
+	else
+		dspcntr |= DISPPLANE_TRICKLE_FEED_DISABLE;
 
 	I915_WRITE(reg, dspcntr);
 
@@ -6768,8 +6770,10 @@ static void ivb_update_cursor(struct drm_crtc *crtc, u32 base)
 			cntl &= ~(CURSOR_MODE | MCURSOR_GAMMA_ENABLE);
 			cntl |= CURSOR_MODE_DISABLE;
 		}
-		if (IS_HASWELL(dev))
+		if (IS_HASWELL(dev)) {
 			cntl |= CURSOR_PIPE_CSC_ENABLE;
+			cntl &= ~CURSOR_TRICKLE_FEED_DISABLE;
+		}
 		I915_WRITE(CURCNTR_IVB(pipe), cntl);
 
 		intel_crtc->cursor_visible = visible;
diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
index 4605682..3a5c0bb 100644
--- a/drivers/gpu/drm/i915/intel_pm.c
+++ b/drivers/gpu/drm/i915/intel_pm.c
@@ -4950,8 +4950,6 @@ static void haswell_init_clock_gating(struct drm_device *dev)
 			I915_READ(GEN7_SQ_CHICKEN_MBCUNIT_CONFIG) |
 			GEN7_SQ_CHICKEN_MBCUNIT_SQINTMOB);
 
-	g4x_disable_trickle_feed(dev);
-
 	/* WaVSRefCountFullforceMissDisable:hsw */
 	gen7_setup_fixed_func_scheduler(dev_priv);
 
diff --git a/drivers/gpu/drm/i915/intel_sprite.c b/drivers/gpu/drm/i915/intel_sprite.c
index 78b621c..ad6ec4b 100644
--- a/drivers/gpu/drm/i915/intel_sprite.c
+++ b/drivers/gpu/drm/i915/intel_sprite.c
@@ -260,8 +260,11 @@ ivb_update_plane(struct drm_plane *plane, struct drm_crtc *crtc,
 	if (obj->tiling_mode != I915_TILING_NONE)
 		sprctl |= SPRITE_TILED;
 
-	/* must disable */
-	sprctl |= SPRITE_TRICKLE_FEED_DISABLE;
+	if (IS_HASWELL(dev))
+		sprctl &= ~SPRITE_TRICKLE_FEED_DISABLE;
+	else
+		sprctl |= SPRITE_TRICKLE_FEED_DISABLE;
+
 	sprctl |= SPRITE_ENABLE;
 
 	if (IS_HASWELL(dev))
-- 
1.8.1.2